The present invention relates to lever mechanisms particularly adapted for use in presses and the like which is characterized by nobel features of construction and arrangement providing progressive transmission of increased delivery force in the operation of the press.
Conventional presses for punching, embossing or deep drawing and the like generally comprise a main frame including a base which supports a die or stationary mechanism component and a ram adapted for reciprocating movement which mounts a tool or movable mechanism component and cooperates with the die to punch, emboss or deep draw a work piece to form a product. The ram and base plate typically mount means or devices for supporting exchangeable tools and dies. The efficiency of the press is limited among other things by the maximum pressing force and the stroke. Usually for economical reasons, the press or machine needed by a given industry is oftentimes purchased with respect to their efficiency according to the current production of the industry. However, it has been found that products are often developed which cannot be processed any longer on the available press or machine devices by reason of the fact that the product requirements exceed the technical specifications of the press. Usually the limiting factor is the available pressing force.
With the foregoing in mind, it is an object of the present invention to provide a lever mechanism as an auxilliary or add-on device for presses which has the capability of increasing the pressing force without necessitating large structural changes in the press itself or substantially shortening the stroke of the ram. To this end, the lever mechanism comprises a generally triangular lever yoke with fulcrums provided adjacent the corners of the triangle, one of which is pivotally connected with the movable mechanism component by means of an equilibrium arm or link, the second is pivotally connected with the retaining plate and the third is pivotally connected with the support plate by means of another equilibrium arm or link.
By this lever mechanism, there is provided an increase in the pressing force which operates according to the laws of leverage. For example, the pressing force initiation takes place from the ram via the attached retaining plate to one of the corner fulcrums of the lever yoke. Since the second corner fulcrum of the lever yoke is connected with the support plate by means of an eqilibrium or balancing arm or link, the third fulcrum pivots about the second and displaces the movable mechanism component by means of the equilibrium link. Thus during the conforming stroke movement of the ram, there is a continuous changing of the lever ratios and this constantly changing lever ratio of the lever system results in different transmission ratios for the distance covered by the movable mechanism component. This advantageously results in transmission of a pressing force as a function of the position of the movable mechanism, which as a result of changing the lever ratios may be selected in such a way that a very great force increase only occurs during the actual pressing or forming of the work piece; that is, in the latter part of the ram stroke range. Thus, while the movable mechanism component is moving or guided toward the work piece, almost no force is required so that this step can be completed more rapidly. For this reason, the lever ratios can be selected in such a way that the movable mechanism component compared to the ram covers a larger distance in this range. Stroke loss as a result of force increasing during the initial operating phase of the mechanism components is advantageously compensated for in this way by the extension of the stroke when guiding the movable mechanism component to the work piece. Depending on the design of the lever system, the maximum stroke of the ram provided by the press is only slightly shortened although the lever mechanism provides a manifold pressing force increase.
In accordance with another feature of the invention, the support plate for the stationary mechanism component, that is the die, may be constructed separately from the frame and secured thereto. The reason for this is that oftentimes the stability of the press frame is not sufficient and thereby requires reinforcement by suitable measures. One arrangement is to provide a separate plate meeting the requirements for the support of the stationary mechanism component. The second corner fulcrum of the lever yoke is fastened to this plate by means of the equilibrium or balancing arm. The support plate itself is anchored in a detachable fashion on the press frame by screw fasteners or bolts. The pressing force gained by the lever mechanism according to the present invention is thereby transmitted as tensile force by means of the equilibrium arm to the separate support plate and, therefore, obviates overstressing of the press frame.
In the preferred embodiment of the invention, at least two lever systems disposed symmetrically to the axis of the mechanism components are provided. By reason of this balanced arrangement, there is a meaningful distribution of the forces so that the individual fulcrums of each system only have to transmit a corresponding portion of the total force and, therefore, may be constructed accordingly. A further advantage is that with a uniform arrangement of several lever systems about the axis of the tools, there is a good and accurate guiding of the movable tool mechanism.
In accordance with a further feature of the present invention, axial guide means extending in the direction of movement of the ram is provided. Thus, in applications wherein the two mechanism components, that is, the punch and die, must cooperate very accurately with equidistant axes, for example, in punching, the lever mechanism is provided with an additional axial guide for the movable mechanism component. A slide pin can be installed in the extension of the ram, for example, on which the movable mechanism component can slide in an axial direction. By this arrangement, the levers only have the function of force transmission.
In accordance with still a further feature of the invention, the retaining plate, support plate, the two mechanism components, the lever yokes and the equilibrium may form a unitary assembly which may be assembled and disassembled from the press as an integral unit very easily and economically. This facilitates installation in the press with a minimum of equipment and manipulations. The force ratios are selectively adjusted to the two mechanism components and to the work piece to be produced and accordingly an optimized lever mechanism can be provided as an exchange component.